Highly extendable lift truck upright assemblies present difficult problems with respect to resolving a variety of factors which affect the productivity, product integrity, lift truck capacity and safety, to name a few. Essentially, these demands on the structure are not always resolved to the optimum level in a general application, high lift truck upright, and even less so for one of special application.
A special application for which this present invention is primarily suited is in connection with material handling in the carpet industry. Typically, twelve foot long rolls of carpet will be stored in high racks above the warehouse floor. To reach such heights it is necessary for the lift truck to have a multi-stage, or high lift upright, capable of reaching, at maximum extension, the upper racks for inserting a ram the length of the spool down the center of the carpet roll.
One of the difficulties of multi-stage uprights is the visibility. The operator must look between the rails to see and maneuver the truck. In the high lift condition, he must look through the overhead guard in addition. It is very difficult to accurately position the tip of the ram to line it up with the carpet spool under such conditions.
Also, conventional multi-stage uprights for high lift applications tend to have a vertical height in the collapsed position that is too tall for many doorways and truck trailers.
High lift applications also require larger counterweight. That is to say, a larger lift truck is normally required to mount such uprights because the load center forward of the front axle of the truck, which acts as a fulcrum, is greater.
The special application carpet handler truck requires that the standard fork bar carriage have a carpet ram attachment mounted on the carriage after removing the forks. Since the attachment is not an integral part of the upright and carriage, it increases the distance in front of the axle to the load center, further reducing the capacity of the truck.
Also standard multi-stage uprights tend to have a free lift, which does not take into account the problems in handling carpets. For example, the carriage extends out beyond the sides of the upright; however, with a carpet ram attachment, this additional width can cause obstructions and impair maneuverability of the truck.
Also, at maximum free lift, the top guide rollers of the carriage may extend above the upright tending to cause damage to the ceiling of trailers or other structures. When maneuvering carpet rolls there is a tendency to misjudge where the end of the roll is relative to the rack, or where the end of the ram is relative to the carpet roll when aligning the ram with the spool elevated twenty-seven feet, or more above the floor.
Also, it is not uncommon to have the carpet ram attachment off center to the load carriage causing an unstable condition which is not easily detected until the load is lifted.